DESCRIPTION: Elucidation of the mechanisms of biological oxidation of amines by the various amine oxidases will provide information on active site structure and permit the rational design of efficient and selective mechanism-based (suicide) inhibitors with therapeutic potential. The major focus of the current grant period will be on the flavin-dependent mitochondrial monoamine oxidases (MAO) (Project I) and on the quinone- containing amine oxidases (Project II), one family of which contains copper and the another family of which appears not to contain copper (known as semicarbazide-sensitive amine oxidases). The quinone- containing enzymes appear to utilize a transamination mechanism for deamination of primary amines, whereas electron-transfer, hydrogen-atom- transfer, hydride-transfer, and addition-elimination mechanisms all remain in contention for MAO. One aim of this grant is to address mechanistic questions through the conduct of model studies, and to design and evaluate new probes which might distinguish among candidate mechanisms. Models which mimic the enzyme chemistry of interest can then be used (i) to "screen" novel ideas for inhibitor design, and (ii) to provide reference derivatives for understanding spectral features displayed by the enzymes. Preliminary screening of designed inhibitors will be carried out in the PI's lab, whereas directed studies with pure enzyme preparations will be carried out in collaboration with Professors Greenaway (Clark University), Kagan (Boston University), Dooley (Montana State University), Palcic (University of Alberta), and Edmondson (Emory University). A related interest in regard to the copper amine oxidases is the mechanism of biogenesis of the trihydroxyphenylalanine quinone cofactor from the active-site tyrosine residue. Mechanisms for copper- mediated phenol oxygenation and possibly copper catalysis of the subsequent oxidation/hydration steps will be assessed in model studies.